Conventionally, lighting columns, comprising generally of aluminium tubes, are secured in use to a ground anchored flange plate.
The top of the column typically has a bracket (usually a single or double bracket) or spigot secured thereto.
A retrofit bracket includes, for example, one or more bracket arms bonded to a cast section which is itself secured to the top of the lighting column. The or each bracket arm is generally formed as an aluminium tube and is fitted over an appropriate end of the casting and welded in place.
Recent surveys and tests have established major concerns over failure caused by fatigue at the weld. High bending moments occur at the bracket exerting considerable stress at the weld.
Moreover, the act of welding results in heat affected zones at the juncture of the bracket arm and cast which can reduce the mechanical properties of aluminium by up to 50%.
Furthermore, the likelihood of fatigue is increased at points where two different metals are welded together, such as for example when aluminium bracket arms are welded to a cast section of the bracket.
The present invention relates to an improved method of securing a bracket arm to a cast section using structural adhesive.
Structural adhesives have generally not been considered for securing brackets and similar components to lighting columns because the adhesive cannot support the weight of the components without support, even when they are held in a jig, and insufficient support may result in a non-uniform layer of adhesive between the substrates.
The present invention seeks to alleviate this problem by providing a recess with boundaries to enable control of the flow of adhesive within the recess thereby to ensure that an even and uniform layer of adhesive is provided across the entire joint.